Expression of connexin57 in mouse development and in harmaline-tremor model.

Connexin57 (Cx57) was previously reported in retinal cells but not in brain nerve cells. This occurrence was tested in this study, by searching for the expression of Cx57 RNA and protein transcripts during the postnatal development of the mouse CNS. Both the Cx57 RNA (investigated by reverse transcriptase-polymerase chain reaction (RT-PCR)) and the protein (Western-Blot and immunohistochemistry using a polyclonal antibody generated in chicken) transcripts were firstly expressed in the late postnatal development (P12). The expression of Cx57 in adult life (studied at P28, by in situ hybridization and immunohistochemical analysis) concerned few regions of the brain stem (inferior olive, lateral reticular nucleus and motor trigeminal nucleus), the cerebellum (Purkinje cells and cerebellar nuclei) and the spinal cord (alpha-motoneurons). Double immunohistochemical studies using the Cx57 antibody and antibodies, which specifically labelled neuronal nuclei (NeuN) and astrocyte cells glial fibrillary acidic protein (GFAP), showed the expression of Cx57 segregated in neuronal cells. The study also confirmed the expression of Cx57 in the horizontal cells of the retinal outer plexiform layer, reported in previous investigations. Given the expression of Cx57 in the cerebellum and pre-cerebellar nuclei, such as olivary and lateral reticular nuclei, a possible role of Cx57 was hypothesized in the electrical coupling of the cerebellum. This hypothesis was tested by searching for the expression of the Cx57 transcripts in the mouse cerebellum of the harmaline-tremor model. The up-regulation of the Cx57 transcripts reported in this model suggested a possible involvement of Cx57 in the electrotonic coupling of the cerebellar system.